Alzheimer's disease (AD) represents an enormous and growing public health problem, due in large part to the fact that there are no effective therapies. A major roadblock to the treatment of AD is the lack of adequate diagnostic tools. Diagnosis is generally based on cognitive decline, which is not necessarily specific to AD. Furthermore, clinically-measurable cognitive decline in AD is thought to manifest after significant neuronal damage has already occurred, precluding the implementation of treatments at early stages of disease before irreversible neuronal damage has taken place. Current methods of diagnosis that allow early detection of AD (brain imaging to detect amyloid-beta (Aβ) deposits and measurement of cerebrospinal fluid levels of Aβ) are expensive, invasive, and have limited availability. An accessible plasma biomarker that provides an AD diagnosis at early stages of disease would therefore be of great benefit to assist with AD diagnosis. The present disclosure meets these and other needs.